chore: LDAP config improvements (#3522)

* chore: Drop management of `SASLAUTHD_*` ENV

- `variables-stack.sh` does not need to manage all these extra ENV or store them. They're not used anywhere else.
- `saslauthd.sh` is the only consumer of these ENV which are effectively direct key/value mappings, with some defaults provided / inherited.

Instead of trying to conditionally support key/value pairs when ENV is set, we could instead use `sed` to delete lines with empty values.

* chore: Drop fallbacks + update configs to match docs

- Drop deprecated support:
  - `DOVECOT_HOSTS` is an ENV deprecated since v10.
  - Fallback for missing URI scheme introduced for Dovecot and SASLAuthd in v10.
  - Adding error log message when no LDAP URI scheme is detected for the supported ENV (when set).
- Docs updated for ENV to reflect the mandatory requirement. `mailserver.env` partially synced equivalent sections.
- Provided base LDAP configs (for overriding) likewise updated from `domain.com` to `example.com`.
- LDAP test updated for required `ldap://` URI scheme. Common ENV shared across LDAP configs hoisted out of the Postfix group.

* chore: Remove unset lines in generated `saslauthd.conf`

target/postfix/ldap-aliases.cf

@@ -1,9 +1,9 @@
 bind             = yes
-bind_dn          = cn=admin,dc=domain,dc=com
+bind_dn          = cn=admin,dc=example,dc=com
 bind_pw          = admin
 query_filter     = (&(mailAlias=%s)(mailEnabled=TRUE))
 result_attribute = mail
-search_base      = ou=people,dc=domain,dc=com
-server_host      = mail.domain.com
+search_base      = ou=people,dc=example,dc=com
+server_host      = mail.example.com
 start_tls        = no
 version          = 3

target/postfix/ldap-domains.cf

@@ -1,9 +1,9 @@
 bind             = yes
-bind_dn          = cn=admin,dc=domain,dc=com
+bind_dn          = cn=admin,dc=example,dc=com
 bind_pw          = admin
 query_filter     = (&(|(mail=*@%s)(mailalias=*@%s))(mailEnabled=TRUE))
 result_attribute = mail
-search_base      = ou=people,dc=domain,dc=com
-server_host      = mail.domain.com
+search_base      = ou=people,dc=example,dc=com
+server_host      = mail.example.com
 start_tls        = no
 version          = 3

target/postfix/ldap-groups.cf

@@ -1,9 +1,9 @@
 bind                     = yes
-bind_dn                  = cn=admin,dc=domain,dc=com
+bind_dn                  = cn=admin,dc=example,dc=com
 bind_pw                  = admin
 query_filter             = (&(mailGroupMember=%s)(mailEnabled=TRUE))
 result_attribute         = mail
-search_base              = ou=people,dc=domain,dc=com
-server_host              = mail.domain.com
+search_base              = ou=people,dc=example,dc=com
+server_host              = mail.example.com
 start_tls                = no
 version                  = 3

target/postfix/ldap-senders.cf

@@ -1,9 +1,9 @@
 bind             = yes
-bind_dn          = cn=admin,dc=domain,dc=com
+bind_dn          = cn=admin,dc=example,dc=com
 bind_pw          = admin
 query_filter     = (mail=%s)
 result_attribute = mail, uid
-search_base      = ou=people,dc=domain,dc=com
-server_host      = mail.domain.com
+search_base      = ou=people,dc=example,dc=com
+server_host      = mail.example.com
 start_tls        = no
 version          = 3

target/postfix/ldap-users.cf

@@ -1,9 +1,9 @@
 bind             = yes
-bind_dn          = cn=admin,dc=domain,dc=com
+bind_dn          = cn=admin,dc=example,dc=com
 bind_pw          = admin
 query_filter     = (&(mail=%s)(mailEnabled=TRUE))
 result_attribute = mail
-search_base      = ou=people,dc=domain,dc=com
-server_host      = mail.domain.com
+search_base      = ou=people,dc=example,dc=com
+server_host      = mail.example.com
 start_tls        = no
 version          = 3